1. Field of the Invention
The present invention relates to a roller bearing and, in particular, to a roller bearing such as a cylindrical roller bearing and a conical roller bearing which is able to maintain proper lubrication between the end faces of a large number of rollers and the collar portion of the roller bearing.
2. Description of the Related Art
FIG. 5 shows a conventional conical roller bearing 50. This conical roller bearing 50 includes an outer race 52 with an outer raceway 51 formed on the inner peripheral surface thereof, an inner race 54 with an inner raceway 53 formed on the outer peripheral surface thereof, a large number of rollers 55 respectively interposed between the outer and inner raceways 51 and 53, and a collar portion 56 formed so as to extend along the axial-direction end portion of the inner raceway 53.
Each of the outer and inner raceways 51 and 53 is crowning machined to thereby have a bus consisting of a concave-shaped arc line. By the way, in the conical roller bearing 50, differently from a self-aligning roller bearing, the center C1 of the bus of the outer raceway 51 is set at an arbitrary position which is shifted from the axis C of the conical roller bearing 50.
Each of the rollers 55 is structured in the following manner: that is, a rolling surface thereof is formed substantially in a conical shape which includes a convex-shaped arc line as a bus, a large-diameter end face 57 thereof is formed as a convex-shaped spherical surface, and a small-diameter end face 58 thereof is formed so as to have an arbitrary surface shape.
These rollers 55 are respectively arranged in such a manner that their respective rotation axes C2 (about which they can be rotated) extend along the bus of a first virtual conical surface having a vertex C3 at a given position existing along the extension line of the axis C of the conical roller bearing 50.
In the thus structured conical roller bearing 50, escape portions 60, each having a section substantially three quarters (xc2xe) of which are composed of a circle, are successively formed along an entry corner existing between the inner raceway 53 and the collar surface 59 of the collar portion 56.
And, as shown in FIG. 6, in the conical roller bearing 50 that rotates normally, due to a previously given pre-load or a component of a bearing load, the large-diameter end face 57 consisting of a convex-shaped spherical surface is slidingly surface contacted with the collar surface 59 consisting of a conical surface through a contact area A having a given area (see hatching shown in FIG. 6).
By the way, generally, the outer raceway 51, inner raceway 53 and rollers 55 of the conical roller bearing 50 are formed such that their buses are respectively composed of arc lines; and, therefore, in case where an excessive load, a biased load, or sudden acceleration is applied to the conical roller bearing 50, a strange phenomenon called a skew or a tilt is easy to occur in the conical roller bearing 50.
Here, the xe2x80x9cskewxe2x80x9d means a phenomenon in which the rotation axis C2 of each roller 55 is inclined or skewed along the spiral direction of the above-mentioned first virtual conical surface. On the other hand, the xe2x80x9ctiltxe2x80x9d means a phenomenon in which the rotation axis C2 of each roller 55 is inclined or tilted with respect to the bus of the above-mentioned first virtual conical surface as well as in the other inclined directions than the inclined direction of the skew phenomenon.
Now, FIGS. 7A and 7B show two states in which a skew and a tilt occur in the conventional conical roller bearing 50, respectively. That is, as shown in FIG. 7A, in case where a skew occurs in the conical roller bearing 50, since the direction of the large-diameter end face 57 consisting of a three-dimensional curved surface varies with respect to the collar surface 59 consisting of a two-dimensional curved surface, the contact area A is moved to the edge portion side of the large-diameter end face 57 as well as to the outside diameter side of the collar surface 59 (see hatching shown in FIG. 7A).
Then, in the conical roller bearing 50, in case where the skew occurs excessively, there is a possibility that the contact area A can deviate from the outside diameter side of the collar surface 59 and thus the contact area between the large-diameter end face 57 and collar surface 59 can be reduced (see a two-dot chained line shown in FIG. 7A).
In this case, when compared with a case where the conventional conical roller bearing 50 rotates normally, since the contact pressure of the contact area A (that is, pressure per unit area) increases, there is a fear that scoring or seizure can occur in one or both of the large-diameter end face 57 and collar surface 59.
On the other hand, as shown in FIG. 7B, in case where a tilt occurs in the conical roller bearing 50 (see hatching shown in FIG. 7B), similarly to the case in which the skew occurs, the contact area A is moved to the outside diameter side of the collar surface 59.
Therefore, in the conventional conical roller bearing 50, in the case of occurrence of an excessive tilt as well, the contact area A is moved to the outside diameter side of the collar surface 59, thereby raising a fear that scoring or seizure can occur in one or both of the large-diameter end face 57 and collar surface 59.
Also, in the conventional conical roller bearing 50, for a structural reason that the large-diameter end face 57 consisting of a spherical surface is slidingly surface contacted with the collar surface 59 consisting of an arc surface by preload, the contact area A has an upper limit, whereby it is difficult to reduce the contact pressure of the contact area A.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional conical roller bearing. Accordingly, it is an object of the invention to provide a roller bearing in which scoring or seizure is hard to occur in rollers and a collar portion respectively forming the components of the roller bearing.
In attaining the above object, according to a first aspect of the invention, there is provided a roller bearing, including: an outer race with a concave-shaped outer raceway formed on the inner peripheral surface thereof; an inner race with a concave-shaped inner raceway formed on the outer peripheral surface thereof; a plurality of substantially cylindrical-shaped rolling elements respectively interposed between the outer raceway and the inner raceway; and, a collar portion formed so as to extend along one of an axial-direction end portion of the outer raceway and an axial-direction end portion of the inner raceway. The outer peripheral surface of each of the rolling elements being formed of a convex-shaped bus, and the end faces of the rolling elements are formed as a convex-shaped spherical surface. The central portion of one of the outer and inner raceways, and the outer peripheral surface of each of the rolling elements is formed of a first bus which has a given radius of curvature and, two end portion sides adjoining the central portion are each formed of a second bus having such a radius of curvature that causes the two end portion sides to part away from the other of the outer and inner raceways, and the outer peripheral surface of each of the rolling elements. The collar surface of the collar portion is formed as a concave-shaped spherical surface.
Also, according to a second aspect of the invention, there is provided a roller bearing, including: an outer race with a convex-shaped outer raceway formed on the inner peripheral surface thereof; an inner race with a convex-shaped inner raceway formed on the outer peripheral surface thereof; a plurality of substantially cylindrical-shaped rolling elements respectively interposed between the outer raceway and the inner raceway; and, a collar portion formed so as to extend along one of an axial-direction end portion of the outer raceway and an axial-direction end portion of the inner raceway. The outer peripheral surface of each of the rolling elements is formed of a concave-shaped bus, and the end faces of the rolling elements are formed as a convex-shaped spherical surface. The central portion of one of the outer and inner raceways, and the outer peripheral surface of each of the rolling elements is formed of a first bus which has a given radius of curvature and, two end portion sides adjoining the central portion are each formed of a second bus having such a radius of curvature that causes the two end portion sides to part away from the other of the outer and inner raceways, and the outer peripheral surface of each of the rolling elements. The collar surface of the collar portion is formed as a concave-shaped spherical surface.
Here, the present invention can be applied to, for example, a radial roller bearing such as a cylindrical roller bearing and a conical roller bearing, or a thrust roller bearing, while the shape of the rolling elements and the number of rows of the rolling elements can be selected arbitrarily.
By the way, referring further to the arrangement of the first and second buses which are used to form the outer and inner raceways and rolling elements, in order to control an increase in the contact pressure in the mutual boundary area, the first and second buses may be structured such that they can share a tangent in common, or there may be provided a third bus in such a manner that it bridges over the boundary line between the first and second buses.
In the conventional roller bearing, since the end face of each roller consisting of a convex-shaped spherical surface is theoretically point contacted with the collar surface consisting of a conical surface and also they are surface contacted with each other due to a pre-load or a component of a bearing load, the sliding contact area of a contact area is limited.
On the other hand, in the roller bearing according to the invention, because the collar surface of the collar portion is composed of a concave-shaped spherical surface, for example, in case where the radius of curvature of the collar surface is set so as to correspond to the radius of curvature of the roller end face, the collar surface and the roller end face are surface contacted with each other. Therefore, whether a pre-load or a component of a bearing load is present or not, the sliding contact area of the contact area can be secured by a given amount or more.
And, in the thus structured roller bearing, by applying a pre-load or a component of a bearing load thereto, the sliding contact area of the contact area can be enlarged over the conventional roller bearing, which can reduce the contact pressure of the contact area compared with the conventional roller bearing, and thus, lower the possibility that scoring or seizure can occur in one or both of the roller end face and collar surface.